This invention relates to prostheses. More particularly, this invention relates to new prostheses and methods for safely and effectively restraining such prostheses using a combination of direct immediate attachment to stabilize the prostheses while attachment to native connective tissue by ingrowth to the prostheses proceeds naturally over time.
Implants or prostheses are employed for restoring damaged upper and lower extremity bones such as fingers, wrists, elbows, knees and ankles of human patients. These prostheses are especially useful in the reconstruction of joints which, for example, have been damaged by pathological conditions such as rheumatoid arthritis, degenerative arthritis, aseptic necrosis, and for treating trauma which may have a debilitating effect on articular joints.
Extra articular bone segment replacement includes long bones replaced after destruction processes, such as trauma and tumors. For example, if a segment of femur (thigh) or radius (forearm) bone shafts is being destroyed by malignant tumor, it may be replaced by a transplanted cadaver bone graft of that segment. Native tendons with connected muscles may be reattached to that bone graft to preserve the function of limb motion. Similarly, a synthetic bone replacement, such as one made of ceramic or metal, could be used to replace those segments.
Unfortunately, some joint implant designs available currently or described in the past have drawbacks arising from their construction and design. For example, current and past scaphoid and lunate carpal bone replacements generally cannot reproduce the normal and vital kinematics of that joint, normally dictated by native ligamentous restraints.
Joint replacement designs or arthroplasties which rely solely on man-made mechanical restraint mechanisms of various types (e.g. semi-constrained elbow arthroplasties), also may fail to properly simulate or replace native ligamentous and capsular restraints. Many arthroplasties also attempt to change the native biomechanical properties of the replaced joint instead of reproducing the native properties. New prostheses which restore native biomechanical properties are discussed and claimed in the present inventor""s U.S. Pat. Nos. 5,702,468 and 5,888,203, which are incorporated by reference.
There are three types of arthroplasties: 1) unconstrained, 2) semi-constrained and 3) fully constrained. A common flaw with all of these current joint replacement designs is the inability to reconstruct and re-attach the replaced joint""s vital native capsular and ligamentous restraints, which dictate, in large measure, the behavior and stability of the joint (i.e., its kinematics).
The present invention may apply to any synovial or diarthroidial human joint, or to extra-articular bone segment replacement. One preferred application of the invention is to joints whose motion and stability are both quantitatively and qualitatively significant and therefore functionally important.
The definitions of xe2x80x9cjointsxe2x80x9d and xe2x80x9carticulationsxe2x80x9d, adopted from Stedman""s Medical Dictionary, 1982, pp. 126-7 and p. 737, refer to three types of xe2x80x9carticulationsxe2x80x9d: fibrous, cartilaginous, and synovial. The synovial articulation is the preferred application of this invention. A synovial articulation (or diarthrodial joint) is a joint allowing various amounts and types of motion in which the bony surfaces are covered with a layer of hyaline or fibrous cartilage. There is a joint cavity containing synovial fluid and lined with a synovial membrane, reinforced by a fibrous capsule and by ligaments.
In order to better explain the vital importance of the natural capsular and ligamentous restraints in a synovial joint, and to illustrate the shortcomings of arthroplasties which do not reconstruct these native restraints, replacement of wrist carpal bones will be discussed below. This discussion will illustrate the anatomy, function and kinematics of the carpus with an emphasis on demonstrating the necessity and unique contribution of the invention as it applies to replacing the scaphoid and lunate carpal bones. This invention, however, is not limited to scaphoid and lunate prostheses but rather extends to all upper and lower extremity arthroplasties in any synovial or diarthroidial joints which are functionally important, as well as to extra-articular bone segment replacement.
Wrist movement is apportioned between the radiocarpal and midcarpal joints in a very complex manner. Accordingly, it is essential that a carpal implant be restrained in a manner as close as possible to that achieved with the native carpal bones and native capsule and ligaments in order to maintain the normal kinematics of the carpus. This serves to preserve the shape of the implant and to prevent wear, fracture, dislocation and particulate synovitis.
To date, a satisfactory technique for reconstruction of native restraints (capsule, ligament and tendon) with arthroplasties has not been achieved. The present invention is uniquely designed to allow the surgeon to accurately and predictably replace native connective tissue restraints and thus prevent the above-mentioned causes of failure.
Accordingly, an object of the present invention is to provide an improved method and prostheses for replacing upper or lower extremity bone(s) in a joint of a human.
A further object of the present invention is to provide an improved method and prostheses for replacing extra-articular bone segments, that is, segments of bones outside of human bone joints.
It is another object of the present invention to provide prostheses for replacing upper or lower extremity bone(s) of a joint in which the prostheses are further restrained using ingrown native ligament, capsule, and tendon.
It is yet another object of the present invention to provide prostheses for replacing upper or lower extremity bone joints as well as extra-articular bone segments in which the reconstruction of native connective tissue restraints encourages normal joint global kinematics, and tendon-muscle function, respectively.
It is a further object of the present invention to provide a method and prostheses for replacing upper or lower extremity bone joints as well as extra-articular bone segments by direct immediate attachment to ligament, capsule, bone, or tendon adjacent the bone or portion of which is to be replaced by the prosthesis while ingrowth adhesion from native ligament, capsule, or tendon to discrete ingrowth receptive zones of the prosthesis proceeds naturally over time, preferably with substantial vascularized tissue ingrowth at the ingrowth receptive zones.
These and other objects and advantages of the invention will appear hereinafter.
The present invention accomplishes the foregoing objects by providing a surgically implantable bone prosthesis including a body member, means for direct immediate attachment of the body member, and at least one ingrowth receptive stationing site on and/or within the body member for delayed ingrowth adhesion naturally over time. The direct immediate attachment of the body member as well as the ingrowth which proceeds over time is to adjacent native connective tissue (ligament, capsule or tendon).
The body member is made totally or partially from any appropriate material including but not limited to a bio-compatible, medically inert material such as ceramic, titanium, a stainless steel alloy, a non-ceramic substrate with a ceramic or other biocompatible, medically inert coating, or an open-celled lattice tantalum metal-carbon foam composite material. The body member may comprise a single component or body member as illustrated in FIGS. 1-15a, or it may be made up of at least two components or body members (e.g. FIGS. 16-18) contoured to resemble the shape of a bone, bones or a portion of a bone or bones which are to be replaced by the prosthesis.
In order to achieve the desired tissue ingrowth over time, the body member must be buttressed and affixed to adjacent connective tissue. Mooring means are provided to draw connective tissue to the ingrowth surface of the stationing site achieving the desired buttressing/affixation. Furthermore, adhesive with impregnated bone or connective tissue ingrowth factors could be used to add strength for temporary holding power as tissue ingrowth progresses over time. The greater the contact area of connective tissue to the implant ingrowth surface of the stationing site, the greater the effectiveness of the natural tissue ingrowth over time. The mooring means preferably significantly reduce relative motion between the implant and/or the adjacent connective tissue and bone, further promoting stable progressive biologic ingrowth over time.
Conventional sutures, anchors, interference screws, medical staples or other external mooring means may serve as mooring means to buttress and affix the body member to adjacent connective tissue or bone. Alternatively, the mooring means can be ligamentous means, which are natural or artificial, and porous or non-porous, including but not limited to local tissue, autografts, allografts, xenografts and synthetic grafts. In one preferred embodiment, the ligamentous means may be a porous woven fabic which is tissue ingrowth receptive. In another preferred embodiment, ligamentous means in the form of natural tissue such as capsular strips, bone-ligament-bone graft, or tendon, may be used. When bone-ligament-bone grafts are used, the volume of the bone portions of the bone-ligament-bone grafts may be enhanced with synthetic bone pastes such as Norian(copyright). When suture or ligamentous means are used, the suture or ligamentous means preferably are affixed to adjacent native ligament or capsule, or to the surrounding native cancellous bone itself to achieve the buttressing/affixation to the ingrowth surface of the stationing site. Sutures, interference screws or adhesive (including inert and biologic adhesives) can be used to affix ligamentous means to adjacent native ligament or capsule or to the surrounding native cancellous bone.
The stationing sites preferably will emulate cancellous bone and will be at locations on the body member corresponding generally to the areas where connective tissue naturally attaches in vivo to bones or portions of bones which are to be replaced by the prosthesis. Additionally, the stationing sites preferably will be of a size and shape corresponding generally to the size and shape of the metaphyseal or diaphyseal areas of bone to which the connective tissue is attached in vivo to the bones or portions of bones which are to be replaced by the prosthesis.
The stationing sites may be treated with humeral growth factors to further tissue induce ingrowth. In addition to the bone and connective tissue ingrowth factors, the stationing sites may be treated with biologic adhesives such as fibrin glue to improve the hold of the mooring means.
In one preferred embodiment, at least one body member of the prosthesis includes a pair of generally parallel channels through which the mooring means can be passed to draw connective tissue to the ingrowth surface stationing site adjacent to the channel openings. In another preferred embodiment, at least one body member includes a channel which loops into and back out of the surface of the body member and the mooring means is passed through this looping channel to draw connective tissue to the ingrowth surface stationing site adjacent to the channel openings. The mooring means used may be conventional suture or ligamentous means as described above.
When mooring means in the form of ligamentous means or suture are passed through channels in a body member to buttress/affix the body member to adjacent connective tissue or bone, such mooring means (which preferably are not attached to the channels before implantation) moor the body member but allow it controlled translational gliding motion (by virtue of elasticity if the attached connective tissue) emulating at least some of the native kinematics of the bone or bones being replaced. The resulting tethering and suspension of the body member prevents undesired excessive motion of the implant and thereby maintains the positional relationship of its ingrowth surface(s) to attached connective tissue. This stabilization encourages undisturbed ingrowth of attached native connective tissue into the stationing sites to proceed naturally over time.
In a still further embodiment of the invention, mooring means in the form of ligamentous means or suture may be physically anchored in one or more channels. This may be achieved by physically attaching the suture or ligamentous means to the channel wall (e.g., by adhesive, anchors, interference screws, etc.). It may also be achievedxe2x80x94over timexe2x80x94using ligamentous means and providing ingrowth receptive zones on the walls of the channel (an example of ingrowth surfaces within the body member), so that attachment by ingrowth proceeds while the ligamentous means are anchored to the channel ingrowth surface using the above-mentioned means of anchoring (e.g.; interference screws).
Alternatively, one bone end of each of a pair of bone-ligament-bone grafts can be anchored in the channels with permanent or dissolving interference screws or anchors, and/or with adhesive. In this case, it is preferred that the anchored bone of two grafts at opposite ends of a channel will touch. Over time, the touching ends of both bone-ligament-bone grafts will grow together producing a single bone-ligament-bone-ligament-bone ligamentous means mooring the body member. Indeed, if ingrowth surfaces are made available in the channel, this complex of bone-ligament-bone-ligament-bone ligamentous means will over time itself adhere and grow into the channel ingrowth surface, adding to the anchorage and stability of the implant.
In another embodiment of the invention, the mooring means may be secured to the periphery of the body member. When mooring means in the form of ligamentous means or suture are used, securement may be by way of eyelets in the surface of the body member, by way of permanent or dissolving interference screws or anchors, with the use of adhesive, by molding the ligamentous means (or suture) in place during formation of the body member, or by other means. When mooring means in the form of ligamentous means are used, the ligamentous means also may be secured to the periphery of the body member with a biologic adhesive such as fibrin glue, with or without connective tissue ingrowth factors.
The body member may be stabilized as explained in my U.S. Pat. Nos. 5,702,468 and 5,888,203, by suspending it on ligamentous means or suture along at least two crisscrossing, preferably substantially perpendicular axes, thereby further restraining the body member to limit translation and destructive shear of the implant short term while permitting limited necessary movement of the body member (e.g., rotation of scaphoid implant) in relation to adjacent bones as ingrowth proceeds from the connective tissue to the stationing sites, naturally over time.
The above, as well as other objects and advantages of the invention, will become apparent from the following detailed description of the preferred embodiments as illustrated in the accompanying drawings.